MacOS下Rails执行generate controller命令报GemNotFound错误求解

问题场景 #

• 系统环境：MacOS，使用rbenv管理Ruby版本，Ruby版本为2.6.3，Rails版本为6.1.4.x
• 复现步骤：
  1. 执行rails new my-app创建项目成功
  2. 进入项目目录执行rails s启动服务成功，可正常访问localhost:3000默认页
  3. 执行rails g controller home index时抛出如下错误：

Traceback (most recent call last):
    20: from /Library/Ruby/Gems/2.6.0/gems/spring-2.1.1/bin/spring:49:in `<main>'
    19: from /Library/Ruby/Gems/2.6.0/gems/spring-2.1.1/lib/spring/client.rb:30:in `run'
    18: from /Library/Ruby/Gems/2.6.0/gems/spring-2.1.1/lib/spring/client/command.rb:7:in `call'
    17: from /Library/Ruby/Gems/2.6.0/gems/spring-2.1.1/lib/spring/client/server.rb:9:in `call'
    16: from /Users/marcoscampos/.rbenv/versions/2.6.3/lib/ruby/site_ruby/2.6.0/rubygems/core_ext/kernel_require.rb:85:in `require'
    15: from /Users/marcoscampos/.rbenv/versions/2.6.3/lib/ruby/site_ruby/2.6.0/rubygems/core_ext/kernel_require.rb:85:in `require'
    14: from /Library/Ruby/Gems/2.6.0/gems/spring-2.1.1/lib/spring/server.rb:9:in `<top (required)>'
    13: from /Users/marcoscampos/.rbenv/versions/2.6.3/lib/ruby/site_ruby/2.6.0/rubygems/core_ext/kernel_require.rb:85:in `require'
    12: from /Users/marcoscampos/.rbenv/versions/2.6.3/lib/ruby/site_ruby/2.6.0/rubygems/core_ext/kernel_require.rb:85:in `require'
    11: from /Library/Ruby/Gems/2.6.0/gems/spring-2.1.1/lib/spring/commands.rb:4:in `<top (required)>'
    10: from /Library/Ruby/Gems/2.6.0/gems/spring-2.1.1/lib/spring/commands.rb:33:in `<module:Spring>'
     9: from /Users/marcoscampos/.rbenv/versions/2.6.3/lib/ruby/site_ruby/2.6.0/rubygems/core_ext/kernel_require.rb:85:in `require'
     8: from /Users/marcoscampos/.rbenv/versions/2.6.3/lib/ruby/site_ruby/2.6.0/rubygems/core_ext/kernel_require.rb:85:in `require'
     7: from /Library/Ruby/Gems/2.6.0/gems/bundler-2.2.26/lib/bundler/setup.rb:20:in `<top (required)>'
     6: from /Library/Ruby/Gems/2.6.0/gems/bundler-2.2.26/lib/bundler/ui/shell.rb:88:in `silence'
     5: from /Library/Ruby/Gems/2.6.0/gems/bundler-2.2.26/lib/bundler/ui/shell.rb:136:in `with_level'
     4: from /Library/Ruby/Gems/2.6.0/gems/bundler-2.2.26/lib/bundler/setup.rb:20:in `block in <top (required)>'
     3: from /Library/Ruby/Gems/2.6.0/gems/bundler-2.2.26/lib/bundler.rb:149:in `setup'
     2: from /Library/Ruby/Gems/2.6.0/gems/bundler-2.2.26/lib/bundler/runtime.rb:18:in `setup'
     1: from /Library/Ruby/Gems/2.6.0/gems/bundler-2.2.26/lib/bundler/definition.rb:228:in `specs_for'
/Library/Ruby/Gems/2.6.0/gems/bundler-2.2.26/lib/bundler/definition.rb:490:in `materialize': Could not find sqlite3-1.4.2, puma-5.4.0, bootsnap-1.7.7, byebug-11.1.3, nio4r-2.5.8, msgpack-1.4.2, bindex-0.8.1, nokogiri-1.12.3, websocket-driver-0.7.5, sassc-2.4.0, ffi-1.15.3, racc-1.5.2 in any of the sources (Bundler::GemNotFound)

对应的Gemfile内容如下：

source 'https://rubygems.org'
git_source(:github) { |repo| "https://github.com/#{repo}.git" }

ruby '2.6.3'

gem 'rails', '~> 6.1.4', '>= 6.1.4.1'
gem 'sqlite3', '~> 1.4'
gem 'puma', '~> 5.0'
gem 'sass-rails', '>= 6'
gem 'webpacker', '~> 5.0'
gem 'turbolinks', '~> 5'
gem 'jbuilder', '~> 2.7'

gem 'bootsnap', '>= 1.4.4', require: false

group :development, :test do
  gem 'byebug', platforms: [:mri, :mingw, :x64_mingw]
end

group :development do
  gem 'web-console', '>= 4.1.0'
  gem 'rack-mini-profiler', '~> 2.0'
  gem 'listen', '~> 3.3'
  gem 'spring'
end

group :test do
  gem 'capybara', '>= 3.26'
  gem 'selenium-webdriver'
  gem 'webdrivers'
end

gem 'tzinfo-data', platforms: [:mingw, :mswin, :x64_mingw, :jruby]

根因说明 #

这个错误是Spring预加载服务缓存了错误的Ruby环境路径导致的：启动Rails服务时用的是rbenv管理的用户级Ruby环境，gem包安装在用户目录下；但调用rails generate命令时，Spring调用了系统自带的Ruby，系统Ruby路径下没有安装项目需要的对应版本gem，因此抛出找不到依赖的错误。 #

解决步骤 #

按顺序执行以下操作即可：

1. 停止当前运行的Spring服务，清除缓存：

spring stop

2. 校验当前Ruby环境是否为rbenv管理的2.6.3版本：

which ruby
# 预期输出为 /Users/你的用户名/.rbenv/shims/ruby，若输出为/usr/bin/ruby则说明用的是系统Ruby
ruby -v
# 预期输出为 ruby 2.6.3 相关版本信息

如果环境不匹配，执行以下命令切换：

rbenv local 2.6.3
rbenv rehash

3. 重新安装项目所有依赖：

bundle install

如果安装原生gem（如sqlite3、ffi）时报编译错误，先安装Xcode命令行工具后重试：

xcode-select --install

4. 重新执行控制器生成命令：

rails g controller home index

内容的提问来源于stack exchange，提问作者mcgha